The present invention relates to a drill head.
Drill heads for rock drills have cutting edges made of a cutting material, preferably a hard metal, and are embodied, for example, as solid carbide drill heads or drill heads made of several parts. Hard metal should be understood in the present case to mean sintered or molten carbides, silicides, borides or their alloys.
The rock drills equipped with a drill head are normally used in connection with axial-impact-supported rotary drills, particularly hand-operated drills, and are used as a rule for the rotary percussive creation of bore holes or through holes in concrete or masonry. The axial impacts are delivered on the shank end of the rock drill inserted into the tool receptacle and initiated via the shank as well as the drill head in the substrate that is being processed. In this way the substrate is processed in a scraping and chiseling manner and reduced chip-by-chip. In addition to the high requirements with respect to the achievable drilling progress and the required expenditure of energy, rock drills should also have the highest possible service life.
A rock drill is known from German Patent Document No. DE 197 24 373 A1, which has a drill shank with at least one removal groove running helically along its longitudinal extension for removed drill cuttings. Furthermore, the rock drill has a drill head made totally of hard metal, which is connected with the front end of the drill shank. The drill head has a major cutting edge as well as at least one minor cutting edge, each of which are arranged along diagonals of the drill head. The major cutting edge extends in the radial direction up to a first diameter, whereas the minor cutting edge extends in the radial direction up to a second diameter, which is smaller than the first diameter. The minor cutting edge in this case, projects axially over the peripheral region of the major cutting edge.
When drilling on rebar, essentially only the major cutting edge removes the rebar and consequently represents the lion's share of the removal rate which produces a high level of stress on the cutting edge.
The object of the present invention is therefore to create a drill head for rock drills, in which the chip removal is optimized and which enables a higher drilling speed on rebar.
According to this, the minor cutting edge and the diameter-determining major cutting edge are arranged on the drill head such that an enveloping surface of the minor cutting edge projects completely axially over an enveloping surface of the major cutting edge (diameter-determining in this case means that the major cutting edge determines the diameter of a drill hole produced with the drill). Because of this measure, when the drill is in operation, the cutting of any rebar that is tapped by drilling is distributed over all cutting edges. In this case, the minor cutting edge removes a portion of the rebar, and the major cutting edge the remainder.
In addition, experiments have shown that a drill with a drill head according to the invention no longer drifts or runs laterally in the event of an impact with rebar so that pins can also easily be used in drill holes with rebar impacts. Furthermore, the drill head has a reduced tendency to get stuck on rebar.
In an advantageous embodiment of the invention, the drill head has precisely two major cutting edges and two minor cutting edges, whereby the cutting behavior is further improved.
A cutting behavior that is further optimized is produced if the at least one major cutting edge runs at a right angle to the at least one minor cutting edge.
The at least one major cutting edge as well as the at least one minor cutting edge each run advantageously linearly.
The invention is depicted in the drawings in one exemplary embodiment.